1. Field of the Invention
The invention relates to an apparatus and method for measuring residual stress in metals and other crystalline materials and the amount of second phase such as austenite in irons and steel by X-ray diffraction, and more particularly to an apparatus and method for measuring non-destructively the residual stress in Titanium and Nickel alloyed materials.
2. Description of the Prior Art
U.S. Pat. No. 3,402,291, entilted Method and Apparatus of Measuring Residual Stress and the Amount of a Known Constituent, issued to Eric W. Weinman on Sept. 17, 1968, teaches an invention which advances the measurement of residual stress and percent retained austenite from a slow laboratory procedure to automatic determination within seconds permitting continuous monitoring of residual stress and percent austenite in production parts. In accordance with this invention, two X-ray sources simultaneously radiate first and second X-ray beams at selected angles of incidence with a common specimen area. Individual detecting devices are provided for measuring background intensity and for automatically locating the true peak positions of the first X-ray beam as diffracted from martensite and austenite planes parallel to the specimen surface and the true peak position of the second X-ray beam as diffracted from equivalent martensite planes oblique to the specimen surface. A device indicates the residual stress as a function of the diffraction angle locations of the martensite diffraction peaks and another device indicates percent retained austenite as a function of the austeniste and martensite diffraction peaks as a function of the relative intensities thereof, which is the measured intensity less the background intensity.
The prior art apparatus includes a device that has two X-ray sources which are placed at different angles to simultaneously irradiate a common area of the sample. The device also has two sets of detector tubes. The output of each set drives a null-seeking mechanism that locates two points of equal corrected intensity for each peak. Corrections for angle-dependent factors are made electrically so that the output of the two detector tubes in a set are proportional to true intensities. At the null point, the true peak position lies midway between the two detector tubes. Poteniometers driven by the gear system at the end of each detector arm indicate the 0.degree. and 45.degree. peak position directly. The recorder is calibrated to read directly in psi because the difference between these voltages is proportional to stress.
The non-destructive X-ray analysis of stress in iron and steel has been very successful, but until presently no one has been able to measure residual stress in Titanium or Nickel alloyed materials using the device of U.S. Pat. No. 3,402,291. The inventor has determined that much redesign and modification of this device must be done in order to measure residual stress in a Titanium alloyed material.